This invention relates to capstans for use in tape transports and in particular to a capstan suitable for use in a tape transport forming part of a video tape recorder.
Capstans for sophisticated tape transports, particularly those incorporated as part of video tape recorders, are required to have high performance, so that they can drive a tape at accurate and controllable speeds. Various designs of capstan are suitable for this general purpose. However, there is a need for a new design, particularly for use in a battery portable video tape recorder in which small size and simplicity of construction have to be fulfilled as well as the requirements of high performance.
It is accordingly a general object of the invention to provide an improved tape driving capstan.
It is a preferred object of the invention to provide a tape drive capstan of simple and compact construction, including its own motor yet providing shielding for the magnetic fields of the motor.
A further aspect of the invention lies in the use of a brushless DC motor for driving the capstan. Such a motor is capable of reliable, quiet performance at high efficiency and it is accordingly a further object of the invention to provide a capstan which includes the relatively rotatable elements of a brushless DC motor.
A further aspect of the invention lies in the incorporation in the capstan of a tachometer assembly. In order to provide servo-mechanical control of a tape capstan, it is necessary to monitor the speed of rotation of the capstan by means of a tachometer in order by comparison of a signal derived from the tachometer and a reference signal to derive an error signal which may be used to energise a power amplifier which drives the capstan, the servo-mechanism being arranged to regulate the speed of the capstan within close limits. A further aspect of the invention is therefore to provide a capstan which includes its own tachometer in a convenient manner.